The present invention generally relates to tire pressure sensors and more particularly to extending the lifetime of a battery of a tire pressure sensor disposed in a tire.
Various types of tire pressure sensors have been developed that are situated within tires of vehicles (see, e.g., U.S. Pat. Nos. 5,540,092 and 5,987,980). These tire pressure sensors require electrical power to monitor and transmit information regarding the current tire pressure for display in the passenger compartment of the vehicle. Typically, the tire pressure sensors are powered by long-life batteries also disposed within the tires. The lifetime of these long-life batteries, however, is five to ten years, which is less than the life span of many automobiles and trucks. The effective lifetime of these batteries may be even shorter, because it is not desirable to run the battery down to such an extent that the tire pressure sensor system fails before the battery is replaced. Furthermore, replacing a tire pressure sensor battery is a labor-intensive process, involving, e.g., the removal of the tire from the wheel.
Accordingly, some tire pressure systems attempt to extend the life of the battery by providing a centrifugal switch disposed between the tire pressure sensor and the battery. This centrifugal switch is activated only when the tires rotate beyond a certain rate. As a result, the battery is used for monitoring tire pressure only when the vehicle is in motion. Another approach to extend the life of the battery is to limit the transmission of the tire pressure information only to certain conditions, for example, if there is a drop in tire pressure or if the tire pressure information is requested by the driver.
These approaches, however, are difficult to model statistically and therefore guarantee a reliable battery lifetime that is commensurate with the life span of the vehicle under a wide range of uses. For example, vehicles in interstate trucking are in motion to a much greater extent than pleasure or commuting vehicles.
Another problem with these approaches is that the usefulness of the tire pressure sensor is curtailed. For example, when the centrifugal switch is used, the tire pressure can only be sensed when the vehicle is in motion. As another example, when the transmission of tire pressure information is limited to certain, rare conditions, the driver of the vehicle cannot be provided with real-time information on the pressure of the vehicle""s tires.
Therefore, there is a need for extending the life of a battery of a tire pressure sensor and for avoid the necessity of replacing a tire pressure sensor battery. There is also need for making tire pressures useful in more situations, e.g. when the vehicle is standing still.
These and other needs are addressed by the present invention, in which the tire pressure sensor battery is recharged through the tire valve. For example, a recharging device may be shaped so that the device would mate with the tire valve and, when activated, cause a rechargeable battery in the tire pressure sensor to be recharged. The recharging device can be used by dealers and mechanics at regular service intervals to ensure that the tire sensor battery is recharged. Advantageously, the effective life of the battery is extended each time the battery is recharged and without having to remove the tire. The ability to recharge the battery through the value stem renders the use of the centrifugal switch optional, thereby permitting the tire pressure to measured even if the vehicle is standing still.
Accordingly, one aspect of the present invention pertains to a device for charging a battery of a tire pressure sensor within a tire. The device includes an electrical power source and an electrode adapted to be coupled to a valve stem of the tire and configured to supply power from the electrical power source to the valve stem for charging the battery. In one embodiment, the device also includes a switch configured for selectively supplying power from the electrical power source to the electrode for charging the battery.
Another aspect relates to a method for charging a battery of a tire pressure sensor disposed in a tire, in which an electrode is applied to a valve stem of the tire and electrical power is supplied to the electrode for charging the battery. In one embodiment, the electrode is disposed upon a device that also has a switch. When the switch in a first position, the electrode can be applied to a valve stem of the tire for reading an indication of a life of the battery, and when the switch in a second position, the electrode can be applied to a valve stem of the tire for supplying electrical power to the electrode for charging the battery.
Still another aspect of the present invention pertains to a tire pressure sensor system, comprising a tire pressure sensor, a rechargeable battery coupled to the tire pressure sensor, and a valve stem assembly that has a pair of electrodes. The electrodes are coupled to the rechargeable battery for accepting electrical power for recharging the rechargeable battery. In one implementation, one of the electrodes is adapted to be coupled to a plunger of a valve stem, and the other of the electrodes is adapted to be coupled to a threaded connector of the valve stem. The tire pressure sensor system may also comprise a centrifugal switch coupled to the tire pressure sensor, in which the electrodes are coupled between the centrifugal switch and the rechargeable battery.
To replace a valve stem in yet another aspect of the present invention, an electrode of the valve stem is disconnected from a lead coupled to a terminal of the battery. The valve stem is replaced, and an electrode of the replaced valve stem is connected with the lead coupled to a terminal of the battery.